Artificial intelligence for improved skin tightening

ABSTRACT

A system (20) includes a plurality of electrodes (28), one or more radiofrequency (RF) generators (30), and a controller (36). The controller is configured to treat skin of a user (22), using one or more decision rules, responsively to multiple ascertained values of at least one parameter, by iteratively ascertaining at least one respective value of the ascertained values, by applying at least one of the decision rules to the ascertained value, identifying a treatment setting from among multiple treatment settings, and causing the RF generators to cause one or more RF currents to pass, through the skin, between at least some of the electrodes in accordance with the identified treatment setting. The controller is further configured to modify at least one of the decision rules in response to the ascertained values. Other embodiments are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/733,911, which was filed on Dec. 1, 2020 in the national phase ofInternational Application PCT/IB2019/054797, filed Jun. 10, 2019, whichclaims the benefit of U.S. Provisional Appl. No. 62/683,070, entitled“Constant RF energy density for skin tightening—therapeutic method andapparatus,” filed Jun. 11, 2018. The respective disclosures of theaforementioned applications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to the field of cosmetics, andparticularly to the treatment of skin.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 8,700,176 describes skin treating devices and systems fordelivering radiofrequency (RF) electromagnetic energy to the skin. Thedevices include one or more electromagnetic RF generating units,multiple RF electrode groups and a controller for controllably applyingRF energy to the skin through any selected RF electrode group or anyselected RF electrode group combination selected from the multiplegroups. The electrodes may be stationary and/or movable electrodes.Different RF frequencies and/or frequency bands may be used.

SUMMARY OF THE INVENTION

There is provided, in accordance with some embodiments of the presentinvention, a system including a plurality of electrodes, one or moreradiofrequency (RF) generators, and a controller. The controller isconfigured to treat skin of a user, using one or more decision rules,responsively to multiple ascertained values of at least one parameter,by iteratively ascertaining at least one respective value of theascertained values, by applying at least one of the decision rules tothe ascertained value, identifying a treatment setting from amongmultiple treatment settings, and causing the RF generators to cause oneor more RF currents to pass, through the skin, between at least some ofthe electrodes in accordance with the identified treatment setting. Thecontroller is further configured to modify at least one of the decisionrules in response to the ascertained values.

In some embodiments, the controller is configured to modify the at leastone of the decision rules using artificial intelligence.

In some embodiments, a different respective one of the RF generators isconnected to each one of the electrodes.

In some embodiments,

the electrodes include at least three electrodes, at least one pair ofthe electrodes being spaced farther apart from one another than isanother pair of the electrodes,

the treatment settings specify respective groups of the electrodes foractivation, and

the controller is configured to cause the RF generators to cause the RFcurrents to pass between the group of the electrodes specified, foractivation, by the identified treatment setting.

In some embodiments, at least some of the treatment settings specify,for activation, different respective ones of the groups.

In some embodiments,

the treatment settings further specify respective sets of phases, atleast some of the treatment settings specifying different respectiveones of the sets for the same one of the groups, and

the controller is configured to cause the RF generators to cause the RFcurrents to pass between the group of the electrodes by causing the RFgenerators to apply respective RF signals to the group of theelectrodes, the RF signals having, respectively, the set of phasesspecified by the identified treatment setting.

In some embodiments, the system further includes a surface shaped todefine a track,

at least one of the electrodes is moveable along the track,

at least some of the treatment settings specify different respectiveinter-electrode separations, and

the controller is configured to cause the RF generators to cause the RFcurrents to pass between the at least some of the electrodes inaccordance with the identified treatment setting by:

-   -   moving the moveable electrode along the track such that the        moveable electrode and another one of the electrodes are spaced        apart from one another by the inter-electrode separation        specified by the identified treatment setting, and    -   subsequently to moving the moveable electrode, causing the RF        generators to cause the RF currents to pass between the moveable        electrode and the other one of the electrodes.

In some embodiments,

the decision rules are represented by a mapping from multiple domains ofthe parameter to the treatment settings, respectively,

the controller is configured to identify the treatment setting byidentifying the domain to which the ascertained value belongs, and

the controller is configured to modify the at least one of the decisionrules by modifying at least one boundary of at least one of the domains.

In some embodiments,

the domains are associated with different respective characteristicvalues, and

the controller is configured to modify the boundary of the at least oneof the domains by:

-   -   modifying the characteristic value of the at least one of the        domains, based on those of the ascertained values belonging to        the at least one of the domains, and    -   setting the boundary responsively to the modified characteristic        value of the at least one of the domains.

In some embodiments, the controller is configured to set the boundary tobe equidistant from (i) the modified characteristic value of the atleast one of the domains, and (ii) the characteristic value of anotherone of the domains that is adjacent to the at least one of the domains.

In some embodiments, the controller is configured to modify thecharacteristic value of the at least one of the domains by:

computing a mean of those of the ascertained values belonging to the atleast one of the domains, and

setting the characteristic value to a weighted average of (i) thecharacteristic value, and (ii) the mean.

In some embodiments,

the ascertained values are first ascertained values, and

the domains include multiple skin-area domains corresponding torespective skin areas,

-   -   each of the skin-area domains corresponding to a respective one        of the skin areas by virtue of having been defined based on        second ascertained values of the parameter associated with the        skin area.

In some embodiments, the skin areas include a cheek and a forehead.

In some embodiments, the domains further include one or moreimproper-electrical-contact domains corresponding to differentrespective states in which the electrodes are not in proper electricalcontact with the skin, and the controller is further configured to:

ascertain another value of the parameter,

ascertain that the other value belongs to one of theimproper-electrical-contact domains, and

cease treating the skin, responsively to ascertaining that the othervalue belongs to the improper-electrical-contact domain.

In some embodiments, the states include a state in which the electrodesare not in any electrical contact with the skin.

In some embodiments, the states include a state in which the electrodesare in electrical contact with the skin but not via a layer of gelhaving a thickness within a predefined range.

In some embodiments, the controller is further configured to generate anoutput indicating the state to which the improper-electrical-contactdomain corresponds.

In some embodiments, the system further includes a temperature sensorconfigured to measure a temperature of the skin and to generate atemperature-sensor output responsively thereto, the ascertained valuesinclude temperature-values of the temperature, and the controller isconfigured to ascertain the temperature-values responsively to thetemperature-sensor output.

In some embodiments, the system further includes an electric-currentsensor configured to measure at least some of the RF currents and togenerate an output responsively thereto, and the controller isconfigured to ascertain the ascertained values responsively to theoutput.

In some embodiments, the ascertained values includeelectric-current-property-values of a property of the at least some ofthe RF currents.

In some embodiments, the system further includes a voltage sensorconfigured to measure a voltage associated with at least some of the RFcurrents and to generate a voltage-sensor output responsively thereto,and the controller is configured to ascertain the ascertained valuesresponsively to the voltage-sensor output.

In some embodiments, the ascertained values includevoltage-property-values of a property of the voltage.

In some embodiments, the ascertained values include impedance-values ofan impedance of the skin.

In some embodiments,

the controller is further configured to cause the RF generators, priorto treating the skin, to cause a pre-treatment electric current to pass,through the skin, between any pair of the electrodes, and

the controller is configured to ascertain an initial one of theascertained values based on the pre-treatment electric current.

In some embodiments, the system further includes a server configured tocommunicate with the controller over a computer network, and the serverand the controller are configured to cooperatively carry out a processthat includes:

comparing a quantity derived from the ascertained values to a baselinequantity, and

responsively to the comparing, generating an output to the user.

In some embodiments, the output includes a message indicating anattribute of the skin.

In some embodiments, the output includes a recommendation for askin-care product.

There is further provided, in accordance with some embodiments of thepresent invention, a method including, using one or more decision rules,treating skin of a user responsively to multiple ascertained values ofat least one parameter, by iteratively ascertaining at least onerespective value of the ascertained values, by applying at least one ofthe decision rules to the ascertained value, identifying a treatmentsetting from among multiple treatment settings, and causing one or moreradiofrequency (RF) currents to pass, through the skin, between at leastsome of a plurality of electrodes in accordance with the identifiedtreatment setting. The method further includes modifying at least one ofthe decision rules in response to the ascertained values.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system for treating skin of auser, in accordance with some embodiments of the present invention;

FIGS. 2-3 are schematic illustrations of techniques for treating skin ofa user in accordance with various treatment settings, in accordance withsome embodiments of the present invention;

FIG. 4A is a flow diagram for an iterative method for treating skin, inaccordance with some embodiments of the present invention; and

FIG. 4B is a flow diagram for post-treatment processing, in accordancewith some embodiments of the present invention.

DETAILED DESCRIPTION Overview

When the dermis layer of skin is heated to around 50-52° C., thecollagen fibers in the dermis remodel, thus causing the skin to becometightened. Hence, some skin-tightening techniques involve heating theskin by applying RF energy to the skin. The RF energy may be applied,for example, using a handheld treatment head comprising a pair ofelectrodes. In particular, RF currents may be passed between the pair ofelectrodes while the electrodes are in electrical contact with the skin,such that the RF currents penetrate the skin.

In general, the depth to which each RF current penetrates is anincreasing function of the distance between the electrodes. For example,the penetration depth for a pair of cylindrical electrodes may beapproximately half the distance between the pair. Hence, a challenge,when using the same RF device to tighten multiple areas of skin, is thatthe depth of the skin that is to be treated—and hence the desiredpenetration depth of the RF currents—may vary from one area to the next.For example, while the deepest portion of the dermis in the cheek orchin may be between 0.2 and 3 mm from the surface of the skin, thedermis in the forehead may be no deeper than between 0.1 and 1 mm. Thus,a penetration depth that is appropriate for the cheek may be dangerousfor the forehead, while a penetration depth appropriate for the foreheadmay be ineffective for the cheek.

To overcome this challenge, the inter-electrode distance (or“separation”) may be varied in accordance with the depth of the skin.For example, a first pair of electrodes at a larger distance from oneanother may be used to treat the cheek, while a second pair ofelectrodes at a smaller distance from one another may be used to treatthe forehead. Alternatively, the distance between a single pair ofelectrodes may be adjusted in accordance with the depth of the skin, bymoving one or both of the electrodes.

The above approach necessitates measuring the depth of the skin duringthe treatment session, or at least measuring a parameter that isindicative of the depth. One such parameter is the impedance of theskin; hence, in theory, the electrodes may be used to measure theimpedance of the skin, and the inter-electrode separation may be variedin accordance with the measured impedance. However, the impedance of anygiven area of skin in one user may be different from that of the samearea of skin in a different user. Moreover, even in a single user, theimpedance of any given area of skin may vary over time.

To address this challenge, in embodiments of the present invention, thehandheld treatment device comprises a controller, configured to applythe RF currents in accordance with particular user-specific decisionrules, and to continually update the decision rules over time, usingartificial intelligence. In particular, during the treatment session,the controller repeatedly ascertains the value of a parameter, such asthe impedance of the user's skin. Based on each ascertained value, thecontroller, using the decision rules, identifies the appropriatetreatment setting—including, for example, the appropriateinter-electrode separation—and then applies one or more RF currents inaccordance with the identified treatment setting. Following thetreatment session, the controller may revise the decision rules, basedon the ascertained parameter values.

For example, for each user, multiple domains of impedance values may bemapped to different respective treatment settings corresponding todifferent respective areas of skin, each pair of adjacent domainsbordering one another at a respective decision boundary. Thus, forexample, for one particular hypothetical user, impedances less than 350Ωmay be mapped to a treatment setting appropriate for the forehead, whileimpedances greater than 350Ω may be mapped to another treatment settingappropriate for the cheek. During the treatment session, the controllermay identify the domain to which each ascertained impedance valuebelongs, and then select the treatment setting to which the domain ismapped. Subsequently to the treatment session, the controller may modifyat least one of the decision boundaries, based on the ascertainedimpedance values.

In some embodiments, to modify the decision boundaries, the controllerfirst updates the “characteristic impedance” Z^(c) of each of the skinareas that was treated, based on the impedance values for the skin areathat were ascertained during the treatment session. In response to theupdated characteristic impedances, the controller may set each decisionboundary to be equidistant from the respective characteristic impedancesof the two skin areas that meet at the decision boundary.

In some embodiments, to update Z^(c), the controller first computes theaverage Z^(a) of the impedance values that were acquired while the skinarea was treated. Subsequently, the controller computes a weightedaverage of the current characteristic impedance and Z^(a), i.e., thecontroller sets the new characteristic impedance, Z^(c)(n), equal toa*Z^(c)(n−1)+(1−α)*Z^(a)(n), where α is, for example, between 0.3 and0.99, e.g., between 0.85 and 0.95. (In some embodiments, the controllerdoes not update Z^(c) unless the skin area was treated for at least apredefined minimum duration, such as one minute, and/or unless apredefined minimum number of impedance values for the skin area wereacquired.)

Typically, upon the user activating the treatment device, the controllerobtains an initial impedance measurement by applying a short RF current,referred to herein as a “prepulse,” to the skin. Based on this initialmeasurement, the controller selects the appropriate treatment setting,and begins the treatment in accordance with this setting. Subsequently,as the regular treatment pulses are applied, the impedance is measuredperiodically, e.g., with a period of between 0.1 and 1 seconds. Based oneach periodic measurement, the controller decides whether to use adifferent treatment setting.

Typically, the controller is further configured to identify situationsin which the electrodes lack proper electrical contact with the skin,such as where the treatment device was lifted from the skin during thetreatment session. In response thereto, the controller may pause or stopthe treatment session.

Typically, the impedance of the skin depends on the amount of moisturein the skin. Hence, in some embodiments, the controller, or acloud-based server, may identify that the skin of the user is dry, basedon the impedance values of the skin that were ascertained during thetreatment session. For example, the controller or server may compare thecurrent characteristic impedance for a particular skin area to abaseline characteristic impedance for the same user, and/or to abaseline characteristic impedance of a group of other users. If thecurrent characteristic impedance deviates from the baseline, a messagerecommending use of a moisturizer may be sent to the user.

System Description

Reference is initially made to FIG. 1 , which is a schematicillustration of a system 20 for treating skin of a user 22, inaccordance with some embodiments of the present invention. In general,system 20 may be used to treat any suitable area of skin, such as skinof a cheek 24, a forehead 26, another portion of the face, an arm, aleg, or an abdomen.

System 20 comprises a handheld skin-tightening device 21, which may bemade from plastic and/or any other suitable material. Device 21comprises a shell (or “case”) 44 coupled to a treatment head 23.Treatment head 23, which is further described below with reference toFIG. 2 , comprises a plurality of electrodes 28. Electrodes 28 aretypically disposed on a distal surface 46 of the treatment head orwithin apertures in distal surface 46, e.g., such that the electrodesprotrude from distal surface 46.

Shell 44 contains one or more RF generators 30 connected to electrodes28, typically via wires 29 passing between shell 44 and treatment head23. Typically, shell 44 further contains a controller (CTRL) 36, amemory 34, and a sensor 32. Typically, RF generators 30, controller 36,memory 34, and sensor 32, along with any one or more of the additionalcomponents described below, are mounted on an electronic circuit board42. In some embodiments, two or more of these components are integratedinto a single chip. For example, device 21 may comprise a chipcomprising both controller 36 and memory 34, such as theCY8C4247LQI-BL473 chip manufactured by Cypress Semiconductor™. In someembodiments, memory 34 comprises both an internal memory, which isintegrated with controller 36 as described above, and an external memorychip.

Typically, controller 36 is configured to perform at least some of thefunctionality described herein by executing firmware and/or softwarecode. Alternatively, the functionality of controller 36 may beimplemented entirely in hardware.

To use device 21, user 22 first covers distal surface 46 (or at leastelectrodes 28) with a layer of gel having a thickness within apredefined range, such as 2-70 mm. Subsequently, the user runs treatmenthead 23 over the user's skin such that electrodes 28 are in electricalcontact with the skin via the gel. As the treatment head is run over theskin, controller 36 treats the skin of user 22 with one or more RFelectric currents, by causing the RF generators to pass the currentsthrough the skin between the electrodes in accordance with feedback fromsensor 32 and data from memory 34.

More specifically, during and/or immediately after the application of atleast some of the electric currents, sensor 32 measures a relevantcharacteristic of the skin or of the electric current, and generates anoutput signal to controller 36 responsively thereto. For example, sensor32 may comprise a temperature sensor, configured to measure thetemperature of the skin during and/or immediately after the applicationof the electric current. (In general, an electric current passed throughthinner skin causes a greater increase in temperature, relative to anelectric current passed through thicker skin.) Alternatively oradditionally, sensor 32 may comprise a current sensor, configured tomeasure the electric current applied to the skin. Alternatively oradditionally, sensor 32 may comprise a voltage sensor, configured tomeasure a voltage associated with the electric current, such as thevoltage at one or more of the activated electrodes, as the current isapplied. Alternatively or additionally, sensor 32 may comprise amoisture sensor, configured to measure the moistness of the skin.Alternatively or additionally, sensor 32 may comprise an optical sensorconfigured to measure optical reflections from the skin, and/or anultrasound transducer configured to measure ultrasound reflections fromthe skin.

Based on the output signal from sensor 32, the controller ascertains thevalue of at least one parameter. For example, based on output from atemperature sensor, the controller may ascertain the temperature of theskin. Alternatively or additionally, based on output from a currentsensor, the controller may ascertain a property, such as the amplitudeand/or phase, of the applied current. Alternatively or additionally,based on output from a voltage sensor, the controller may ascertain aproperty, such as the amplitude and/or phase, of the voltage between theactivated electrodes. Alternatively or additionally, based on outputfrom the aforementioned current sensor and/or voltage sensor, thecontroller may ascertain the impedance of the skin; for example, thecontroller may divide the voltage amplitude measured by the voltagesensor by the current amplitude measured by the current sensor.

Typically, the parameter values are ascertained periodically, e.g., witha period of between several microseconds and one second.

In response to ascertaining each parameter value, the controlleridentifies a treatment setting from among multiple treatment settings,by applying at least one decision rule to the ascertained value. Forexample, the controller may input the parameter value to amachine-learned model such as a decision tree or forest, which isconfigured to select a treatment setting responsively to the input byimplementing a set of decision rules. Alternatively, the decision rulesmay be represented by a mapping from multiple domains of the parameterto the treatment settings, respectively, such that the controller mayidentify the treatment setting by identifying the domain to which thevalue belongs. In other words, as further described below with referenceto FIGS. 2-3 , the controller may identify the domain to which theascertained value belongs, and then identify the treatment setting towhich, per the mapping, the domain is mapped.

In response to identifying the treatment setting, the controller causesthe RF generators to cause one or more RF currents to pass, through theskin, between the electrodes in accordance with the identified treatmentsetting. In particular, if, when the treatment setting is identified, anRF current is already being applied in accordance with the identifiedtreatment setting, the controller causes the application of this currentto continue. (This causation may be active, in that the controller maycommunicate an appropriate control signal to the RF generators such thatthe RF generators continue applying the current, or passive, in that thecontroller may refrain from stopping the RF generators from applying thecurrent.) Otherwise, if an RF current is being applied in accordancewith a different treatment setting, the controller stops the applicationof this current by communicating an appropriate control signal to the RFgenerators. Subsequently, or if no RF current is being applied when thetreatment setting is identified, the controller applies a new RF currentin accordance with the identified treatment setting by communicating anappropriate control signal to the RF generators.

Typically, the peak-to-peak amplitude of each RF current is between 20and 130 V (e.g., between 40 and 55 V). In some embodiments, the RFcurrents are pulsed, e.g., such that the duration of each RFcurrent—which, in these embodiments, may also be referred to as a“pulse”—is between 1 and 1000 ms. (The amplitude and/or duration of eachpulse may be varied, so as to deliver a desired amount of energy to theskin.) Alternatively, a single current may be applied continuously untilthe next treatment setting is identified, or until the treatment sessionis terminated.

During or following each treatment session, the controller may modify atleast one decision rule in response to the ascertained parameter values.For example, if the decision rules are implemented in a machine-learnedmodel, the controller may retrain the model. Alternatively, as furtherdescribed below with reference to FIGS. 2-3 , the controller may modifythe boundary of at least one parameter-value domain stored in memory 34.

Alternatively or additionally to the components described above, device21 may comprise any other suitable components, such as a power button orswitch, a battery configured to power the device, one or morelight-emitting diode (LED) indicators, and/or a movement sensor, such asan accelerometer. In response to the movement sensor ceasing to detectmovement of the device across the skin, the controller may cause thedevice to power off, thus protecting the skin of the user from excessiveelectric current.

In some embodiments, as shown in FIG. 1 , a different respective RFgenerator is connected to each one of the electrodes. (Each RF generatoralso has a connection to ground, which is not shown in the figure.) Insuch embodiments, each electric current is typically generated byapplying one RF signal to one electrode, and another RF signal with thesame amplitude but opposite phase to another electrode. The voltagebetween the pair may then be ascertained by measuring the voltage at oneof the electrodes and multiplying this voltage by two. In otherembodiments, a single RF generator is connected to all of theelectrodes. As yet another alternative, various sets of multipleelectrodes may be connected to different respective RF generators.

In some embodiments, each RF generator operates as a voltage source, inthat the RF generator is configured to apply a predetermined voltage.Nonetheless, since the amplitude of the voltage that is actually appliedmay differ from the predetermined amplitude, e.g., due to the batterythat powers the device being depleted, the applied voltage may bemeasured. Similarly, the applied current may be measured even if the RFgenerator operates as a current source.

In some embodiments, device 21 further comprises a communicationinterface, such as a network interface (not shown), a WiFi interface,and/or a Bluetooth interface. Via the communication interface, thecontroller may communicate with an external processor, such as aprocessor belonging to the user's smartphone and/or a processor 39belonging to a cloud server 38. (Optionally, the controller maycommunicate with processor 39 via the user's smartphone.) At least someof this communication may be exchanged over a suitable computer network40, such as the Internet.

Typically, server 38 further comprises a network interface 37, such as anetwork interface controller (NIC). Via network interface 37, processor39 may communicate with device 21, with the user's smartphone, and/orwith any number of other devices belonging to other users.

In general, each of the processors described herein may be embodied as asingle processor or as a cooperatively networked or clustered set ofprocessors. In some embodiments, the functionality of at least one ofthe processors, as described herein, is implemented solely in hardware,e.g., using one or more Application-Specific Integrated Circuits (ASICs)or Field-Programmable Gate Arrays (FPGAs). In other embodiments, thefunctionality of each processor is implemented at least partly insoftware. For example, in some embodiments, each processor is embodiedas a programmed digital computing device comprising at least a centralprocessing unit (CPU) and random access memory (RAM). Program code,including software programs, and/or data are loaded into the RAM forexecution and processing by the CPU. The program code and/or data may bedownloaded to the processor in electronic form, over a network, forexample. Alternatively or additionally, the program code and/or data maybe provided and/or stored on non-transitory tangible media, such asmagnetic, optical, or electronic memory. Such program code and/or data,when provided to the processor, produce a machine or special-purposecomputer, configured to perform the tasks described herein.

Adaptively Treating the Skin

Reference is now made to FIG. 2 , which is a schematic illustration of atechnique for treating skin of a user in accordance with varioustreatment settings, in accordance with some embodiments of the presentinvention.

In some embodiments, the skin-tightening device comprises at least threeelectrodes, at least one pair of the electrodes being spaced fartherapart from one another than is another pair of the electrodes. In theparticular example embodiment shown in FIG. 2 , for example, fourelectrodes protrude from distal surface 46: a first electrode 28 a, asecond electrode 28 b, a third electrode 28 c, and a fourth electrode 28d. Some pairs of these electrodes have a first inter-electrode spacingd1, others have a second inter-electrode spacing d2, which is greaterthan d1, and another has a third inter-electrode spacing d3, which isgreater than d2. (The spacing between first electrode 28 a and fourthelectrode 28 d is not indicated explicitly in the figure.) As anotherpurely illustrative example, first electrode 28 a may be at a distanceof d3 from each of second electrode 28 b and third electrode 28 c,second electrode 28 b may be at a distance of d1 from third electrode 28c, and fourth electrode 28 d may be at a distance of d2 from each ofsecond electrode 28 b and third electrode 28 c. (Example values forthese distances are 2 mm for d1, 3 mm for d2, and 4 mm for d3.)Alternatively, the electrodes may be of any other suitable number,and/or may be arranged in any other suitable configuration.

In such embodiments, the treatment settings stored in memory 34 specifyrespective groups of the electrodes for activation. For example, thememory may store a mapping from multiple domains of the relevantparameter, such as the impedance or temperature of the skin, torespective groups of the electrodes for activation. In response toidentifying the treatment setting for each ascertained parameter value,the controller causes the RF generators to cause one or more electriccurrents to pass between the group of electrodes specified, by theidentified treatment setting, for activation.

Typically, at least some of the treatment settings specify differentrespective groups for activation. For example, the hypothetical mappingin FIG. 2 includes four different groups of activated electrodes: (i)the domain [x0, x1) is mapped to the group consisting of first electrode28 a, second electrode 28 b, and third electrode 28 c, (ii) the domain[x1, x2) is mapped to the group consisting of first electrode 28 a,third electrode 28 c, and fourth electrode 28 d, (iii) the domain [x2,x3) is mapped to the group consisting of second electrode 28 b andfourth electrode 28 d, and (iv) the domains [x3, x4) and [x4, x5) areeach mapped to the group consisting of all of the electrodes.

In some embodiments, the treatment settings further specify respectivesets of phases, at least some of the treatment settings specifyingdifferent respective sets of phases for the same group of electrodes. Inresponse to identifying the treatment setting, the controller causes theRF generators to apply respective RF signals to the group of theelectrodes specified by the treatment setting, the RF signals having,respectively, the set of phases specified by the identified treatmentsetting.

For example, in FIG. 2 , although the domains [x3, x4) and [x4, x5) aremapped to the same group of electrodes, these domains are mapped todifferent respective sets of phases. In particular, for the domain [x3,x4), first electrode 28 a and third electrode 28 c have a phase of zero,while second electrode 28 b and fourth electrode 28 d have a phase of180 degrees. (Thus, in accordance with this treatment setting, the RFsignals are applied to the electrodes such that the polarity of firstelectrode 28 a and third electrode 28 c is opposite that of secondelectrode 28 b and fourth electrode 28 d.) For the domain [x4, x5), onthe other hand, first electrode 28 a and fourth electrode 28 d have aphase of zero, while second electrode 28 b and third electrode 28 c havea phase of 180 degrees.

Typically, the domains include multiple skin-area domains correspondingto respective skin areas, each of the skin-area domains corresponding toa respective one of the skin areas by virtue of having been definedbased on values of the parameter associated with the skin area. Forexample, one domain may correspond to a cheek, by virtue of having beendefined based on parameter values associated with a cheek, such as cheekimpedance values. Another domain may correspond to a forehead, by virtueof having been defined based on parameter values associated with aforehead, such as forehead impedance values.

In some embodiments, the parameter values used to define the skin-areadomains are collected during a calibration procedure. During thisprocedure, the user runs the treatment head over the areas of skin forwhich the skin-area domains are to be defined. For each of these areas,RF currents are applied to the area, while the values of the parameterare ascertained.

For example, prior to using the device for treatment, the user may runthe treatment head (with a suitably-thick layer of gel covering theelectrodes) over multiple specific skin areas in sequence, indicating tothe controller (e.g., by pushing a particular button) each transitionfrom one skin area to the next. For each of the skin areas, thecontroller may ascertain a plurality of parameter values, and thendefine the domain for the skin area based on the ascertained values. Forexample, for each skin area, the controller may compute a respectivecharacteristic value (CV), e.g., by computing the average of theascertained values (excluding any outliers). The controller may then setthe boundaries of the domains such that each boundary between adjacentdomains is equidistant from the respective characteristic values of theadjacent domains.

For example, based on the calibration procedure, the controller maycompute a characteristic impedance of Z_(C) for the user's cheek and acharacteristic impedance of Z_(F) for the user's forehead. Responsivelythereto, the controller may set a boundary of (Z_(C)+Z_(F))/2 betweenthe cheek domain and the forehead domain.

In other embodiments, the values are collected from a suitablepopulation of other users. Based on the values, a processor (e.g.,processor 39 (FIG. 1 )) defines a set of default skin-area domains,which may be loaded into the memory of each skin-tightening deviceduring the manufacture thereof.

In any case, regardless of whether the domains are computed from auser-specific calibration procedure or from data obtained from thegeneral population, the boundaries of the domains may be adjustedthroughout the lifetime of the device, as further described below.

In some embodiments, the domains in memory 34 further include one ormore improper-electrical-contact domains corresponding to differentrespective states in which the electrodes are not in proper electricalcontact with the skin. Responsively to ascertaining, during thetreatment, a value of the parameter belonging to animproper-electrical-contact domain, the controller ceases treating theskin, or pauses the treatment until proper electrical contact isrestored.

Typically, at least one of the improper-electrical-contact domainscorresponds to a state in which the electrodes are not in any electricalcontact with the skin. For example, a “gel domain,” which may include,for example, impedances between 550 and 800Ω, may correspond to a statein which the electrodes are covered by a layer of gel having a thicknesswithin the predefined range, but are not in electrical contact with theskin. As another example, an “air domain,” which may include, forexample, impedances higher than 4000Ω, may correspond to a state inwhich the electrodes are not covered by gel and are not in electricalcontact with the skin. As another example, a “short-circuit domain,”which may include, for example, impedances less than 100Ω, maycorrespond to a state in which the electrodes are electrically connectedto each other via a low-resistance conductor, such as the user'swristwatch.

Alternatively or additionally, one of the improper-electrical-contactdomains may correspond to a state in which the electrodes are inelectrical contact with the skin but not via a layer of gel having athickness within the predefined range; in other words, the electrodesmay be covered by too little or too much gel. As a purely illustrativeexample, a domain corresponding to skin contact with too littleintervening gel may include impedances between 1800 and 4000Ω, while adomain corresponding to skin contact with too much intervening gel mayinclude impedances between 100 and 200Ω.

In some embodiments, responsively to identifying a state in which theelectrodes are not in proper electrical contact with the skin, thecontroller generates an output indicating the state. For example, inresponse to identifying an improper amount of gel, the controller maycause an appropriate LED indicator to be lit, such that the userrealizes the need to increase or decrease the amount of gel.Alternatively or additionally, the controller may communicate a messageindicating the state to an external device, such as server 38 (FIG. 1 )or the user's smartphone. Responsively to receiving this message, theexternal device may generate an output to the user indicating the state,along with any action required to resume treatment. For example, in thecase of an improper amount of gel, the user may be instructed toincrease or decrease the amount of gel.

Each of the improper-electrical-contact domains may be defined bypassing RF currents between the electrodes, and ascertaining values ofthe relevant parameter, while the electrodes are in the associated stateof improper electrical contact. Alternatively, at least one of theimproper-electrical-contact domains may be defined based on preexistingdata, such as tables of impedance values for different types ofmaterials. In any case, typically, the same set ofimproper-electrical-contact domains is loaded into the memory of eachskin-tightening device during the manufacture thereof.

During each treatment session, the controller may store, in memory 34,each ascertained value belonging to each domain. Subsequently, followingthe treatment session, based on the stored values, the controller maymodify the respective characteristic values of one or more of thedomains. The controller may then reset at least one of the domainboundaries responsively to the modified characteristic values. Forexample, the controller may set each boundary to be equidistant from thetwo nearest characteristic values.

In some embodiments, the controller modifies the characteristic value ofa domain by computing the mean of the ascertained values belonging tothe domain and then setting the characteristic value to a weightedaverage of the (current) characteristic value and the mean. In otherwords, given a characteristic value CV_(i) and a mean M of theascertained values, the controller may compute a new characteristicvalue CV_(i+1) as αCV_(i)+(1−α)M, where a is a suitable constant betweenzero and one, such as a constant between 0.3 and 0.99, e.g., between0.85 and 0.95.

Alternatively to assigning a single characteristic value to each domain,the controller may assign multiple characteristic values to each domain,e.g., by computing several local averages of a plurality of parametervalues belonging to the domain. In such embodiments, responsively to aplurality of parameter values ascertained during a treatment session,the controller may update one or more of the local averages.Subsequently, the controller may modify the boundary between twoadjacent domains by minimizing the sum of squared distances between theboundary and the local averages in the adjacent domains, or using anyother suitable technique.

Reference is now made to FIG. 3 , which is a schematic illustration ofanother technique for treating skin of a user in accordance with varioustreatment settings, in accordance with some embodiments of the presentinvention.

In some embodiments, surface 46 is shaped to define a track 48, and atleast one electrode 28 e is moveable along track 48, such that theinter-electrode separation “s” between electrode 28 e and anotherelectrode 28 f is adjustable. For example, the moveable electrode may besituated within the track, with the proximal end of the moveableelectrode, which lies beneath surface 46, threaded onto a screw lyingparallel to the track and coupled to a motor. By using the motor to turnthe screw, controller may move the moveable electrode along the track,toward or away from electrode 28 f.

In such embodiments, at least some of the treatment settings stored inmemory 34 specify different respective inter-electrode separations. Forexample, FIG. 3 shows, for the same set of hypothetical domains shown inFIG. 2 , different respective inter-electrode separations s1, s2, s3,s4, and s5. During the treatment session, in response to identifying theappropriate treatment setting, the controller moves electrode 28 e alongthe track such that electrode 28 e and electrode 28 f are spaced apartfrom one another by the inter-electrode separation specified by thetreatment setting. Subsequently to moving electrode 28 e, the controllercauses the RF generators to cause one or more electric currents to passbetween electrode 28 e and electrode 28 f. (It is noted that a treatmentsetting may specify an inter-electrode separation implicitly, byspecifying the position of the moveable electrode with respect to anycoordinate system.)

In general, for such embodiments, the controller may modify thecharacteristic values and/or the boundaries for the domains as describedabove with reference to FIG. 2 .

In some embodiments, treatment head 23 comprises one or more pairs offixed-location electrodes, as in FIG. 2 , together with at least onemoveable electrode, as in FIG. 3 . A treatment setting may thus specifya group of activated electrodes (along with, optionally, respectivephases for the group), together with an inter-electrode separation forthe moveable electrode.

It is noted that the treatment settings may specify additional treatmentparameters not described above with reference to FIGS. 2-3 . Forexample, two treatment settings may specify different respective voltageor current amplitudes.

In some cases, a combination of domains may be mapped to a singletreatment setting. Thus, for example, a particular domain of impedancevalues in combination with a first domain of temperature or moistnessvalues may be mapped to a first treatment setting, while the same domainof impedance values in combination with a second domain of temperatureor moistness values may be mapped to a second treatment setting.

Advantageously, combining an impedance domain with a temperature ormoistness domain may account for the fact that the impedance of skin maybe a function of the temperature or moistness of the skin, such that asingle impedance domain may correspond to different respective areas ofskin at different respective temperatures or levels of moistness.Furthermore, this scheme may facilitate providing multiple treatmentsettings for a single skin area. For example, at the beginning of atreatment session, when the skin temperature is relatively low, a firsttreatment setting, specifying a relatively large number of activatedelectrodes, may be used.

As the session continues and the skin temperature approaches apredefined safety threshold, however, a second treatment setting,specifying fewer activated electrodes, may be used.

Example Algorithms

Reference is now made to FIG. 4A, which is a flow diagram for aniterative method 50 for treating skin, in accordance with someembodiments of the present invention. Method 50 is executed bycontroller 36 (FIG. 1 ) following the powering-on of device 21 (FIG. 1), and, optionally, an input from the user (e.g., via the pressing of anappropriate button) indicating that the user wishes to begin a treatmentsession.

Typically, method 50 begins with a prepulse-applying step 52, at whichthe controller, prior to treating the skin, causes the RF generators tocause a pre-treatment electric current to pass, through the skin,between any pair of the electrodes. (The duration of this “prepulse” istypically between 1 and 20 ms, e.g., between 1 and 5 ms.) In someembodiments, a single pair of electrodes on the treatment head isdesignated for application of the prepulse; in other embodiments, thepair used for the prepulse may vary from one application to the next.

Based on the prepulse, the controller ascertains an initial value of therelevant parameter, such as the temperature of the skin, the amplitudeand/or phase of the prepulse, or the amplitude and/or phase of theinter-electrode voltage, at a parameter-value-ascertaining step 54.Subsequently, at a domain-identifying step 56, the controller identifiesthe domain to which the parameter value belongs.

Next, at a domain-classifying step 58, the controller checks whether theidentified domain is a skin-area domain. If yes, the controller, at asetting-identifying step 60, identifies the treatment setting to which,per the mapping in memory 34 (FIG. 1 ), the identified domain is mapped.In response to identifying the treatment setting, the controller, at acurrent-applying step 62, causes the RF generators to cause one or moreelectric currents to pass, through the skin, between the electrodes inaccordance with the identified treatment setting.

On the other hand, if the identified domain is not a skin-area domain(but rather, is an improper-electrical-contact domain), the controllerdecides, at a deciding step 59, whether to cease treatment of the skin.For example, the controller may ascertain whether the identified domaincorresponds to a state in which the device or the user is at risk ofbeing harmed, such as in the case of a short circuit or of theelectrodes being covered by an insufficient amount of gel. If thecontroller decides to cease treatment, the controller proceeds to apost-treatment processing step 65, described below. Otherwise, thecontroller returns to prepulse-applying step 52. The controller may thusapply repeated prepulses until proper electrical contact is establishedbetween the electrodes and the skin.

Following current-applying step 62, the controller, at aduration-checking step 64, checks whether the duration of the treatmentsession thus far exceeds a predefined safety limit, such as two or threeminutes. If not, the controller returns to parameter-value-ascertainingstep 54. Otherwise, the controller ceases to treat the skin, andproceeds to post-treatment processing step 65. Similarly, as describedabove with reference to FIG. 1 , the treatment may be stopped inresponse to a lack of detected motion of the device. Likewise, thetreatment may be stopped in response to the temperature of the skinexceeding the aforementioned predefined safety threshold, or in responseto the user actively terminating the treatment, e.g., by pressing anappropriate button.

Following the treatment of the skin, the controller performspost-treatment processing step 65, in which the controller, typicallyusing artificial intelligence, modifies at least one boundary of atleast one of the parameter-value domains in response to the parametervalues ascertained during the treatment. In this regard, reference isnow made to FIG. 4B, which is a flow diagram for post-treatmentprocessing step 65, in accordance with some embodiments of the presentinvention.

Post-treatment processing step 65 begins with a first checking step 66,at which the controller checks whether any of the skin-area domainsidentified during the performance of method 50 were not yet processed.If yes, the controller selects an unprocessed identified skin-areadomain, at a domain-selecting step 68. Subsequently, at a secondchecking step 70, the controller checks whether the number of parametervalues ascertained for the selected domain exceeds a predefinedthreshold. If yes, the controller, at a mean-computing step 72, computesthe mean of the parameter values ascertained for the selected domain(excluding any outliers). Subsequently, at acharacteristic-value-modifying step 74, the controller modifies thecharacteristic value for the selected domain, based on the mean. Forexample, as described above with reference to FIG. 2 , the controllermay compute a weighted average of the characteristic value and the mean.Subsequently to characteristic-value-modifying step 74, or if not enoughparameter values were ascertained, the controller returns to firstchecking step 66.

In response to ascertaining, at first checking step 66, that nounprocessed identified skin-area domains remain, the controller, at aboundary-modifying step 76, modifies the boundaries of the skin-areadomains based on the modified characteristic values. For example, asdescribed above with reference to FIG. 2 , the controller may set eachboundary of each skin-area domain to be midway between thecharacteristic value of the domain and the characteristic value of therelevant adjacent domain.

Other Embodiments

In some embodiments, server 38 (FIG. 1 ) and controller 36 areconfigured to cooperatively carry out a process that includes comparinga quantity derived from at least some of the ascertained parametervalues to a baseline quantity, and responsively to the comparing,generating an output to the user, e.g., by sending an email message tothe user's email account or a text message to the user's phone.

For example, the controller may communicate multiple ascertained valuesof the temperature or impedance of at least one area of the user's skinto the server. The server may then compute the mean or median of thesevalues, and compare this quantity to a baseline.

(Alternatively, the controller may compute the mean or median, andcommunicate this quantity to server.) In response to the comparison, theserver may ascertain an attribute of the skin, such as the moistness ofthe skin. Responsively thereto, the server may generate an output to theuser, such as a message indicating the attribute (e.g., a messageindicating that the skin is dry) and/or a recommendation for a skin-careproduct (e.g., a moisturizer). Recommendations for skin-care productsmay also be issued to the user irrespective of the properties of theuser's skin, based on data collected from other users.

Alternatively or additionally, the controller and at least one externalprocessor, such as processor 39 (FIG. 1 ) belonging to server 38 and/ora processor belonging to the user's smartphone, may cooperativelyperform at least some of the functionality described above withreference to the figures. For example, during each treatment session,the controller may communicate each ascertained parameter value to theexternal processor, and the external processor may then identify theappropriate treatment setting and communicate the treatment setting tothe controller. Alternatively or additionally, the post-treatmentprocessing, in which the decision rules are modified, may be performedby the external processor.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1. A system, comprising: a plurality of electrodes; one or moreradiofrequency (RF) generators; and a controller, configured to: usingone or more decision rules, treat skin of a user responsively tomultiple ascertained values of at least one parameter, by iteratively:ascertaining at least one respective value of the ascertained values, byapplying at least one of the decision rules to the ascertained value,identifying a treatment setting from among multiple treatment settings,and causing the RF generators to cause one or more RF currents to pass,through the skin, between at least some of the electrodes in accordancewith the identified treatment setting, and modify at least one of thedecision rules in response to the ascertained values.
 2. The systemaccording to claim 1, wherein a different respective one of the RFgenerators is connected to each one of the electrodes.
 3. The systemaccording to claim 1, wherein the electrodes comprise at least threeelectrodes, at least one pair of the electrodes being spaced fartherapart from one another than is another pair of the electrodes, whereinthe treatment settings specify respective groups of the electrodes foractivation, and wherein the controller is configured to cause the RFgenerators to cause the RF currents to pass between the group of theelectrodes specified, for activation, by the identified treatmentsetting.
 4. The system according to claim 3, wherein at least some ofthe treatment settings specify, for activation, different respectiveones of the groups.
 5. The system according to claim 3, wherein thetreatment settings further specify respective sets of phases, at leastsome of the treatment settings specifying different respective ones ofthe sets for the same one of the groups, and wherein the controller isconfigured to cause the RF generators to cause the RF currents to passbetween the group of the electrodes by causing the RF generators toapply respective RF signals to the group of the electrodes, the RFsignals having, respectively, the set of phases specified by theidentified treatment setting.
 6. The system according to claim 1,further comprising a surface shaped to define a track, wherein at leastone of the electrodes is moveable along the track, wherein at least someof the treatment settings specify different respective inter-electrodeseparations, and wherein the controller is configured to cause the RFgenerators to cause the RF currents to pass between the at least some ofthe electrodes in accordance with the identified treatment setting by:moving the moveable electrode along the track such that the moveableelectrode and another one of the electrodes are spaced apart from oneanother by the inter-electrode separation specified by the identifiedtreatment setting, and subsequently to moving the moveable electrode,causing the RF generators to cause the RF currents to pass between themoveable electrode and the other one of the electrodes.
 7. The systemaccording to claim 1, wherein the decision rules are represented by amapping from multiple domains of the parameter to the treatmentsettings, respectively, wherein the controller is configured to identifythe treatment setting by identifying the domain to which the ascertainedvalue belongs, and wherein the controller is configured to modify the atleast one of the decision rules by modifying at least one boundary of atleast one of the domains.
 8. The system according to claim 7, whereinthe ascertained values are first ascertained values, and wherein thedomains include multiple skin-area domains corresponding to respectiveskin areas, each of the skin-area domains corresponding to a respectiveone of the skin areas by virtue of having been defined based on secondascertained values of the parameter associated with the skin area. 9.The system according to claim 1, further comprising a temperature sensorconfigured to measure a temperature of the skin and to generate atemperature-sensor output responsively thereto, wherein the ascertainedvalues include temperature-values of the temperature, and wherein thecontroller is configured to ascertain the temperature-valuesresponsively to the temperature-sensor output.
 10. The system accordingto claim 1, further comprising an electric-current sensor configured tomeasure at least some of the RF currents and to generate an outputresponsively thereto, wherein the controller is configured to ascertainthe ascertained values responsively to the output.
 11. The systemaccording to claim 10, wherein the ascertained values includeelectric-current-property-values of a property of the at least some ofthe RF currents.
 12. The system according to claim 1, further comprisinga voltage sensor configured to measure a voltage associated with atleast some of the RF currents and to generate a voltage-sensor outputresponsively thereto, wherein the controller is configured to ascertainthe ascertained values responsively to the voltage-sensor output. 13.The system according to claim 12, wherein the ascertained values includevoltage-property-values of a property of the voltage.
 14. The systemaccording to claim 1, wherein the ascertained values includeimpedance-values of an impedance of the skin.
 15. The system accordingto claim 1, wherein the controller is further configured to cause the RFgenerators, prior to treating the skin, to cause a pre-treatmentelectric current to pass, through the skin, between any pair of theelectrodes, and wherein the controller is configured to ascertain aninitial one of the ascertained values based on the pre-treatmentelectric current.
 16. The system according to claim 1, furthercomprising a server configured to communicate with the controller over acomputer network, wherein the server and the controller are configuredto cooperatively carry out a process that includes: comparing a quantityderived from the ascertained values to a baseline quantity, andresponsively to the comparing, generating an output to the user.
 17. Amethod, comprising: using one or more decision rules, treating skin of auser responsively to multiple ascertained values of at least oneparameter, by iteratively: ascertaining at least one respective value ofthe ascertained values, by applying at least one of the decision rulesto the ascertained value, identifying a treatment setting from amongmultiple treatment settings, and causing one or more radiofrequency (RF)currents to pass, through the skin, between at least some of a pluralityof electrodes in accordance with the identified treatment setting; andmodifying at least one of the decision rules in response to theascertained values.
 18. The method according to claim 17, wherein theelectrodes comprise at least three electrodes, at least one pair of theelectrodes being spaced farther apart from one another than is anotherpair of the electrodes, wherein the treatment settings specifyrespective groups of the electrodes for activation, and wherein causingthe RF currents to pass between the at least some of the electrodescomprises causing the RF currents to pass between the group of theelectrodes specified, for activation, by the identified treatmentsetting.
 19. The method according to claim 18, wherein at least some ofthe treatment settings specify, for activation, different respectiveones of the groups.
 20. The method according to claim 18, wherein thetreatment settings further specify respective sets of phases, at leastsome of the treatment settings specifying different respective ones ofthe sets for the same one of the groups, and wherein causing the RFcurrents to pass between the group of the electrodes comprises causingthe RF currents to pass between the group of the electrodes by causingone or more RF generators to apply respective RF signals to the group ofthe electrodes, the RF signals having, respectively, the set of phasesspecified by the identified treatment setting.
 21. The method accordingto claim 17, wherein at least one of the electrodes is moveable along atrack, wherein at least some of the treatment settings specify differentrespective inter-electrode separations, and wherein causing the RFcurrents to pass between the at least some of the electrodes inaccordance with the identified treatment setting comprises: moving themoveable electrode along the track such that the moveable electrode andanother one of the electrodes are spaced apart from one another by theinter-electrode separation specified by the identified treatmentsetting; and subsequently to moving the moveable electrode, causing theRF currents to pass between the moveable electrode and the other one ofthe electrodes.
 22. The method according to claim 17, wherein thedecision rules are represented by a mapping from multiple domains of theparameter to the treatment settings, respectively, wherein identifyingthe treatment setting comprises identifying the treatment setting byidentifying the domain to which the ascertained value belongs, andwherein modifying the at least one of the decision rules comprisesmodifying the at least one of the decision rules by modifying at leastone boundary of at least one of the domains.
 23. The method according toclaim 22, wherein the ascertained values are first ascertained values,and wherein the domains include multiple skin-area domains correspondingto respective skin areas, each of the skin-area domains corresponding toa respective one of the skin areas by virtue of having been definedbased on second ascertained values of the parameter associated with theskin area.
 24. The method according to claim 17, wherein the ascertainedvalues include temperature-values of a temperature of the skin.
 25. Themethod according to claim 17, further comprising measuring at least someof the RF currents and generating an output responsively thereto,wherein the method comprises ascertaining the ascertained valuesresponsively to the output.
 26. The method according to claim 25,wherein the ascertained values include electric-current-property-valuesof a property of the at least some of the RF currents.
 27. The methodaccording to claim 17, further comprising measuring a voltage associatedwith at least some of the RF currents and generating avoltage-indicating output responsively thereto, wherein the methodcomprises ascertaining the ascertained values responsively to thevoltage-indicating output.
 28. The method according to claim 27, whereinthe ascertained values include voltage-property-values of a property ofthe voltage.
 29. The method according to claim 17, wherein theascertained values include impedance-values of an impedance of the skin.30. The method according to claim 17, further comprising, prior totreating the skin, causing a pre-treatment electric current to pass,through the skin, between any pair of the electrodes, wherein the methodcomprises ascertaining an initial one of the ascertained values based onthe pre-treatment electric current.
 31. The method according to claim17, further comprising: comparing a quantity derived from theascertained values to a baseline quantity; and responsively to thecomparing, generating an output to the user.